The invention relates to a method of fumigating agricultural products in storage or transportation facilities for controlling pests with the aid of hydrogen phosphide which thereafter is bound and/or decomposed to a substantial extent.
For the last fifty years or so, hydrogen phosphide has proved to be a valuable fumigating agent for controlling pests in stored argricultural products. Compositions that release hydrogen phosphide have been made commercially available and have found worldwide acceptance since, to name only some of their advantages, they are highly efficient in controlling pests and easy to handle while the residues remaining after fumigation are harmless in ecological respects.
Fumigating compositions of the above type comprise as a major component some metal phosphide such as aluminum phosphide or magnesium phosphide, which hydrolyzes to give hydrogen phosphide under the influence of atmospheric humidity or moisture in the stored products. Such fumigating compositions may comprise additional components which either affect the developing rate of hydrogen phosphide in any desired manner, promote safety (especially when water seeps in), lower the phosphine concentration in the gas thus produced, improve the extent of gas development, or the like. Numerous phosphine-releasing compositions suitable for controlling pests are known, all of which may be used in the method of the invention. The particular form of the fumigating composition is not decisive either; suited are e.g. tablets, pellets, as well as powders packed in individual bags (sachets) or a series of interconnected bags.
Fumigation methods of the type described here are normally employed for controlling pests which attack agricultural products such as feedstuffs, grain, beans, peanuts and tobacco, in conventional storage facilities or transportation facilities such as railroad cars or the cargo holds of barges and ships.
The pests to be controlled in this manner may be rodents, but they usually are insects such as the corn weevil, Australian wheat weevil, saw-toothed grain beetle, grain borer, rice weevil and the like, as well as moths.
Up to now, fumigations were typically conducted in the following manner: Care had to be taken to establishing gas-tight conditions in the storage space containing the products to be fumigated so that phosphine could not escape into the atmosphere. The fumigating agent was then spread out and after the last person had left the respective facility, doors and other openings had to be sealed as well. After an appropriate exposure time during which the hydrogen phosphide could take effect on the parts in the stored products, the storage space had to be thoroughly ventilated to remove the hydrogen phosphide.
In contrast to residual products of the fumigating compositions which are quite harmless to the environment (and to humans) when fumigation is finished, hydrogen phosphide is highly toxic to mammals and humans. Morever, hydrogen phosphide gives off a strong, rather offensive odor reminescent of garlic, that is perceptible even at extremely low concentrations of about 0.02 pmm. Depending on the mode of application and the care taken in sealing off the storage space, hydrogen phosphide may escape into the atmosphere so that people living in the vicinity of the fumigation site will be unduly molested or even physically harmed. As the phosphine concentration cannot be determined by smelling, phosphine odors that suddenly occur (even if the concentration remains below the admissible level) may cause anxiety and sometimes nausea in particularly sensitive people. The same may happen when people approach the storage facility immediately after it has been ventilated in the conventional manner. Finally, in the interest of general protection from emissions of any type, one should always aim at releasing as little hydrogen phosphide as possible into the atmosphere.